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3.3 Design objectives and theoretical approach
Main design objective is to follow and respect the request of the assignment that has been exposed in previous paragraph, which has been always taken as reference direction during the performing of the works, (providing required elaboration). At the same time, coherently with the adopted approach, some additional indications, concerning the philosophical contents of the design, have been developed in order to gain a more mature awareness of the aims and finalities of this delicate and peculiar rehabilitation intervention.
All the theoretical considerations that have been developed have been exposed in the different stages reports, (Inception Report and Phase A report), and given for approval to UNESCO and to the ICE commissions (4th and 5th commissions).
In this type of intervention, and in this historical moment, it is extremely important to define a correct and clear theoretical approach to the design objectives, without which the whole design would be fragile and would have to face frequent incoherences that would invalidate also an operation perfectly correct on the technical side.
3.3.1 Design objectives description
This Pilot Project has been named, in agreement with PCU TA, as "Rehabilitation of the Old Bridge of Mostar" since it is partially composed by different practical approaches: conservation and preservation, remedial and repair interventions, dismantling and remounting operations and reconstruction works. All the above should be aimed at the final rehabilitation and restoring of the Monumental Complex of the Stari Most (Old Bridge) of Mostar.
Main design assumptions:
The recovered stones are, at the moment, the only valuable elements of a great ancient monument, they have historical value, and they represent an interesting example of the ancient technique of assembling voussoirs and a constructive method which should be studied and investigated.
Rehabilitation of the Old Bridge is therefore designed as a:
It has to be strongly underlined that all the above listed items are only main design steps that represent, trough a synthetic and simplified scheme, the objectives of the rehabilitation of the Old Bridge of Mostar. Of course, either to gather a detailed explanation, either to understand which have been the technical and theoretical reasons that have led to the above decisions, it is necessary to refer to the subsequent paragraphs of this chapter, and to the whole chapter 4 of this report.
3.3.2 Design methodology
Design methodology has followed mainly the ToR requirements, and has been developed considering current approach criteria for similar type of rehabilitation interventions. Design has been mainly structured in order to respect the ancient remnants of the Old Bridge and the abutment walls and in order to clearly declare which are the new interventions.
Methodology has referred, moreover, to the requirements asked by the PCU TA, UNESCO and by the ICE and has referred to the International Principles of restoration. In detail we have:
Design methodology has referred, moreover, to the additional principles:
During the several stages of on site surveys and design processing, it has been used exclusively instrumental systems and computer systems. The procedures adopted guarantee the following:
For additional notes about methodology refer to chapter 4 of this report.
3.3.3 Reconstruction work methodology
It should be underlined that the ancient Bridge of Mostar was built following a methodology, a technique and a procedure which was typical of the ancient times, linked to the available construction systems and machinery and which, nowadays, may be only hypothesised. If a similar hypothetical procedure were followed strictly, the final result would be the construction of a similar Old Bridge: in other words, referring mostly to stone layout and to curvature geometry, we would obtain a similar but different structure.
For the above reasons, coherently to the required objectives and aims of the assignment, the design is not trying to re-perform all the hypothetical steps of the ancient yard, (which in most cases happened to be randomly performed, like the sorting of the stone sizes), but it has been found a compromise among ancient methods and final results in order to gain a structure identical to the former one even for what concern many details like stone layout and geometry of the intrados curvatures.
The above mentioned observations mostly concern the stone cut works, (refer to chapter 7 of this report for additional notes), and the new technical devices that will be used: like machinery and provisional structures.
Design objectives are, therefore, aimed at reconstructing an "identical structure", (as required), more than performing nowadays the same hypothetical yard experience of the ancient time, which would be an interesting experience but with remarkable different results and with technological and practical difficulties. (Refer to §4.1.2 for additional notes).
3.3.4 Design technological approach
Design has been developed being well aware of the gap that there is among accuracy worked out in the drawings and practical technical impediments and constraints in performing the works on-site, having to manage the stone as construction material. For the above reasons special devices and procedures have been worked out in order that dimensioning of the different stones and voussoirs would not be so difficult to be performed (refer also to chapter 7 of this report).
Moreover thank to the given tolerances (like quarrying tolerances), and the management of some groups of dimensions trough the range system, (refer also to next paragraph), it will be possible to face this matter that has been defined as "technological issue" of the design.
Geometrical and survey controls about the proceeding of the works will be, for the above reasons, extremely important and will have to be performed constantly while works are ongoing to avoid any incoherence and unforeseeable result. (Refer to §4.1.2 for additional notes).
3.3.5 Methodology for determing ancient assembling criteria
Former bridge stone elements were assembled with metal cramps and dowels sealed with lead poured in purposely built slots. This refine technique has been considered, in the design approach, as one of the most important value to be preserved of the ancient construction: design has therefore studied with detailed accuracy all the peculiarities and the positioning criteria of the above mentioned metal stuff with the declared aim of gathering all the wise devices that were proper of this ancient assembling method. At a first glance, the positioning of the strengthening metal elements may seem to be approximately performed, but with more accurate observations held on the bridge remnants it gets clear that there were some important rules linked to practical and technological requirements for the right functioning of the structure. Before proceeding to final design, studies and surveys have been performed, and for each element it has been determined a range of location measurements and a range of dimensions. The study has led to work out some limit measures to be respected in the positioning of the metal strengthening devices compared to the shapes and dimensions of the stone blocks and their joints. The same method has been consequently applied to the stone blocks and to their carved channels and slots.
Design dimensions and measurements, for the above described devices, have been given with ranges and with limits following the determined ancient criteria; this because it wouldn't have been theoretically correct to give a single average dimension to be repeated identically all over the structure, while, in the ancient bridge, a different method was followed, which was more suitable to the variability of the stone elements depending on the natural availability of the quarry.
3.3.6 Management of small irregularities
Former Bridge was characterised by small irregularities, variations and by ordinary constructive imperfections, of which there is no documentation, (apart from surveys of the Bridge remnants). These small variations are precious and are part of the beauty of the monument and shouldn’t be neglected to guarantee the final global aspect of the bridge. In current design they have been considered and analysed to fulfil to the required aim of reproducing the ancient bridge as it was, and to avoid the construction of a polished structure quite different from the former one. (See §4.2.3 for additional notes). Design, in order to manage correctly the above mentioned features, has given range dimensions for some of the elements that were subjected to variations, (it wouldn’t have been correct to assume an arbitrary measure for them all). At the same time, design has adopted a tolerance systems which allows the possibility of slight variations (in one centimetre range): leaving margins free to be slightly managed during the on site stone assembling, by practical and manual adjustments, similar to the ancient adopted techniques, this way we will guarantee the reproducing of the same level of imperfections of the former bridge. A special system of progressive control has been worked out to make sure, step by step, that we are not going far from the final design and far from the former bridge.
3.3.7 Management of thickness dimensions
The ancient documentation is poor of cross sections and of thickness and projecting dimensions of the elements. This of course constitutes an important limit to the exact global geometry determination, and these elements have of course a remarkable esthetical architectural value. Inaccuracies in the geometry determination of these dimensions may lead to a different global aspects of the monument. (Refer also to §5.7 of this report).
For what concern thickness of spandrel, cornice and parapet elements, dimensions, have been given by range values being unknown and quite variable from the study of the bridge transversal section. Design approach trough range dimensions for the undetermined dimensions is one of the basic philosophical choice of this rehabilitation design and it is aimed at reproducing the same quantity of randomly that was proper of the former structure. Criteria adopted for range dimensions are results of observations of the ancient bridge remaining portions. (Refer also to §7.12.4 of this report).
3.3.8 Declaration of new interventions
One of the most important conceptual risk that we run by reconstructing the bridge, is to confuse the ancient original elements of the abutments and of the bridge remnants with the new interventions. This should not happen for a conceptual coherence, for respect to the ancient left portions, and because history may be not changed: with war, in fact, something has been lost forever and may be not completely restored. The memory of what has happened should not be cancelled and should leave at least a trace also on the Bridge. A refined design plan with marking of some joints and stones, (see drawing AD-03), has been worked out to gain the results with no-shocking devices but with slightly interventions that at a first sight may be not gathered but with an accurate observation they are readable. This marking of the joints and of the stones is required for two different reasons: one is mainly scientific, and related to restoration requirements for which it is important to identify in future times each different intervention on the monument; the other reason is instead historical, and is aimed at preserving the trace and the course of time and events. (Refer also to §4.5 of this report).
3.3.9 Use of new technologies
New technologies will be used for what concern working machinery and provisional structures like centerings, scaffoldings and similar facilities for the yard purposes.
Not the same may be said for the work phases: there will be different foreseen stages in which traditional working and hand made working will have to be performed (like all the finishing, stone final cut and assemblage of metal cramps and dowels).
Construction materials will be equal to the original ones unless structural and safety requirements will impose the use of better performing materials. (This issue will be finalised with the results coming from laboratory tests and consequent structural design).
For the strengthening aim of the structure, modern techniques may be used only for static reasons and only when the ancient constructive method would not be adequate.
3.3.10 The spirit of the works and design limits
No architectural design work will ever be enough to guarantee a perfect result on-site for such a delicate intervention as it is the rehabilitation of the Old Bridge of Mostar. To gain an high level of architecture work, which could compete with the marvellous former monument, all the given technical advises, specifications, warnings and requirements will be useless if rehabilitation is not performed with sensible, careful, humble and respectful attitude. The quality results, final aspect of the structure, architecture details, finishing works, are all in the hands of the Work Supervisor and in the hands of the Workers: with equal technical specifications we could have either the worst, either the best intervention of the kind, depending mostly on the accuracy with which works will be performed.
The spirit with which restoration works should be held is not the same that is used for ordinary construction interventions: money saving, serial organisation, simplifications, time and deadlines are things which absolutely do not match with the requirements of an intervention of this type. Rehabilitation should be held with a spirit of research, of study, of understanding the ancient values, of humble observation of the wise technique used many years ago. If this spirit is not shared by all the members involved in the project, then we will soon loose the real meaning of this work and we will get something which will never satisfy the expectations of the whole cultural World and, what is even worst, of Mostar citizens.
The rehabilitation of the Bridge will have to be conceived also as an important moment for the population of Mostar and of Bosnia: the symbol of the town will be restored after war events, and the construction period will assume the characteristic of a local, quite and thoughtful celebration, (not as a World press event).
Of course when works will be completed, this project will soon lead to develop a cultural interest about the monument and about the history of the town that should be valorised trough the settling of a museum. This design work, among its main objectives, foresees the foundation of a museum either to host the ancient ruins of the Bridge, (plus studies and findings), either to host anything which is related to the history of the town, which is still so little known and spread out. In the museum, two blocks currently stored in Komos depot, n°47 and n°48), could take place, as proposed by Mr Bessac, being traced by carvings of ancient hand-quarrying-work that may has been performed for the Old Bridge voussoirs.
Another matter that should be underlined is about design limits. Limits lie in the fact that, in a restoration design, it can not be possible to define everything at this stage, because it's not possible to know everything about the site and about the ancient ruins: trough investigations we do not get a complete knowledge like the one during on-site excavations. For the above reasons it would not even be correct to try to define and finalise anything concerning the works that may lead to slight design changing and improving. Nevertheless design has tried to give different options for matters that weren't still completely clear.
CREDITS:Intellectual property of this report and of the design drawings is owned by General Engineering s.r.l.
author of the text: arch. Manfredo Romeo – other contributes have been mentioned in related paragraphs
© - General Engineering Workgroup -
Final Design Report
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